High-speed comparators frequently rely on some form of regeneration (positive feedback) to simultaneously achieve high speed and high gain. A latch employing positive feedback is often used as the last stage of high-speed comparators to provide regeneration as well as rail-to-rail swing. The outputs of the half-latch may be driven to either the positive or negative supply in each of its stable states, causing the steady-state gain of the latch to be very low. Typically, an extremely large overdrive voltage is required to change the latch from one stable state to another due to the low gain, and the speed of the latch is also degraded by the relatively slow transition from the low gain region of operation to the high gain region of operation.
In order to mitigate these effects, some form of active restore is generally used to hold the latch in its high gain region until a decision must be made. In situations where a comparator must be continuous, large amounts of pre-amplification are typically required to maintain comparator sensitivity and still generate the overdrive voltages required to drive the latch. However, higher preamplifier gain may cause larger propagation delay due to either a higher gain per stage and/or a higher number of gain stages.